By the way, what brand of panels are they?
> I'm posting this, so it might help someone else.
> WHGN went off 3 times, between 9: 15A and 10:00 A, today, then stayed off.
> This is an HT-20CD, with Digit exciter. It was about noon, before anyone
> could get there. I was hoping to do some stuff at the studio, so asked a
> local contract engineer to look at it. And Dave is a lot closer.
> When he arrived, there were no overloads. The transmitter would begin to
> start up, but the exciter output is muted until the plate voltage is
> applied. Today, the plate would stay on for a couple seconds, then turn
> off. The exciter would not unmute. He was stumped, so I told him to call
> At first, Harris suggested it appeared to be a problem with the controller
> board[s]. The transmitter is originally supplied with a special extender
> board to assist in troubleshooting these cards. Well, before we bought the
> station, I guess someone walked off with the extender. It was mostly
> impossible to reach any test points without the extender. Dave was
> proceeding the best he could. But as the day wore on, the problems were
> becoming worse. Eventually, the plate contactor would not pull in. Still
> no overloads on the panel. Power is ON and the transmitter's meters
> indicate there is normal voltage on each of the three phases. Harris was
> also stumped.
> Well, to shorten the story, here is where we think we are: The transmitter
> has TWO 3-phase breakers: 30A for the transmitter cabinet and 200A for the
> HV cabinet. The voltmeters and phase-loss relay monitor power from the 30A
> breaker. There is no monitor for a phase loss on the 200A feed to the HV
> cabinet. Eventually, we discovered an open phase [one bad pole on the 200A
> panel breaker]. Power is normal on the 30A breaker. There appears to be
> absolutely no indication of overheating to the 200A breaker. Everything
> looks normal. Dave only made one mistake: initially, he was measuring
> voltage to ground, rather than measuring phase-to-phase. There was enough
> current passing to the "dead" phase to cause the high-impedance of his VOM
> to read normal. It was only going back and measuring PHASE-TO-PHASE that
> there was any indication of a problem.
> SO I think all we need to do is install a new wall breaker. But finding a
> 200 A breaker to fit an obsolete panel, may be a challenge.
> That is the task for Wednesday.
> Whoever wired this building should be given 39 lashes with a hot soldering
> iron. There is a 400A/3-phase main, which branches off to a 200A /3-phase
> panel and a 200A single phase panel. All that is on the 3-phase panel is
> one 30A branch breaker for the transmitter and the 200A branch breaker for
> the HV supply. Hmmmm... 200A main breaker, followed by a 200A branch
> breaker... Maybe we could bypass the defective branch breaker,
> temporarily. I am reluctant to do this, but need to get back on the air.
> Yet I do NOT want a photo of this breaker panel posted on There, I Fixed
> It website!
> John S.